Stock material or miscellaneous articles – Composite – Of polyamide
Patent
1995-06-23
1997-11-04
Mosley, Terressa
Stock material or miscellaneous articles
Composite
Of polyamide
2641761, 524322, 524399, 524432, 528324, 528339, B32B 2708
Patent
active
056838174
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The molding process of synthetic resin consists of, first, a step whereby resin supplied from the material supply port (hopper) of the molding machine is melted by heating (plasticization step); second, a step whereby the plasticized resin is made to completely fill the screw groove or mold while kneading by applying shear force (injection/filling step); third, a step whereby the resin placed in the mold is solidified by cooling (cooling step); followed by a step whereby the molded product is discharged from the mold (mold release step).
In a continuous process, the plasticization step and the cooling step are generally conducted simultaneously in these processes. In other words, plasticization of the resin of a molding processing cycle is carried out while the resin placed in the mold in the immediately prior cycle is being cooled in the aforementioned molding processing cycle. Nonetheless, the time necessary for plasticization and cooling is longer than the time necessary for the injection and discharge steps.
Conducting molding at high molding efficiency and maintaining high quality of the molded goods are demanded when producing molded goods by injection molding processes. When using resins that solidify rapidly such as nylon and polystyrene and when molding thin-shaped molded goods, problems, such as short shots, arise because the injection speed slows during molding. Another problem is that injection cannot be continued by melting the resin inside the cylinder of the molding machine in the prescribed cycle time when the plasticization capacity of the resin is low during high cycle operation.
Prior to now, shortening of the plasticization time, which generally accounts for approximately 50% of the molding cycle time, was concluded to be the major factor contributing to shortening the molding processing cycle time to obtain higher productivity while avoiding the aforementioned problems. However, since the cooling time may be shorter than the plasticization time when the heat conductivity of the resin is large, the ability to shorten the plasticization time in some way should be the key to shortening the molding processing cycle. In other words, the molding cycle time, especially the duration of the plasticization step, controls the molding performance and quality of the molded goods. Therefore, attempts were made in the past to accelerate plasticization by raising the screw rotation while lowering the screw backpressure.
A molding method that resolves poor molding and molding defects directly associated with the molding process (such as valleys and short shots) while continually maintaining the necessary molding cycle time while operating the injection molding machine on a high cycle, and elucidation of an improved polyamide resin composition to be used in this method were demanded because of the situation described above. Shortening of the plasticization time while maintaining a high quality of the molded goods was demanded to attain the goal of shortening the molding cycle time.
In the plasticization step of the injection molding process, the resin material, granules, or pellets that have fallen into the heating cylinder for injection under their own weight from the hopper are placed in a molten condition by elevation of the temperature from inside (through the heat of friction generated by the kneading action) together with heat from the outer circumference of the heating cylinder while being mixed and kneaded by the rotations of the screw and carried to the tip of the cylinder through the groove. Molten resin is simultaneously stored in the tip of the heating cylinder. The reaction force (backpressure) of this material pushes the screw backward. The measurement step that determines the mount injected is subsequently carried out by controlling the mount of retraction by a limit switch and stopping the rotation of the screw at a set position.
SUMMARY OF THE INVENTION
In the present invention, it has been discovered that the combined use of an internal lubricant and ext
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AN 86-223567 Abstract.
Supplementary European Search Report for PCT/US/12593, EP 94 90 5528, Jan. 1, 1996.
E. I. Du Pont de Nemours and Company
Mosley Terressa
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